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NEC Quiz: Article 388 Answers

by Mark Lamendola

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  1. This wiring method is the nonmetallic counterpart to the surface metal raceway covered in Article 386. It's a nonmetallic raceway that's supposed to be mounted to the surface of a structure [388.2]. And the requirements for nonmetallic are very similar to those for metallic. An obvious issue is that metallic raceway is conductive and nonmetallic is not; this has implications for bonding requirements and for static control (e.g., use in hazardous locations). Generally, this raceway has very high aesthetic value. It's meant to be installed as a system, using the couplings, connectors, boxes, and fittings for that particular system.

  2. There are two permitted uses (the metallic version has four). The two are: In dry locations and extending through walls and floors (this last one has conditions for permissibility) [388.10]. What is different: The metallic version can also be used in Class I, Division 2 hazardous locations as permitted in 501.10(B)(3) and under raised floors, as permitted in 645.29(1),

  3. There are actually seven uses not permitted. For metallic, there are five.

    What is different: For nonmetallic, one of the two permitted uses missing from the list of four for metallic is moved to the not permitted list for nonmetallic and made more general . It is: in hazardous locations (except as as permitted elsewhere in the NEC). Nothing is said about "under raised floors," so if they are a dry location the NEC permits installation there.

    Plus other five listed for the metallic version (Article 386): Where subject to severe damage; where subject to corrosive vapors; where the voltage between conductors is 300V or more (unless specific special circumstances exist); in hoistways; where concealed (except as permitted in 388.10(2)) [388.12]. Plus one more restriction: For conductors whos insulation temperature would exceed those for which the nonmetallic raceway is listed. This restriction does not explicitly appear in Article 386, but common sense tells us it's there anyhow.

  4. Secure the raceway per the manufacturer's installation instructions [388.30]. Note that deviating from these instructions may well produce an installation that violates the listing of the components. They are meant to be assembled and supported in specific ways, and they are tested with those assembly and support means to get their testing lab listing.
  5. You can use only listed components [388.6]. Maybe something you'd normally use for EMT would handily solve an installation problem, but using it would render the installation out of compliance with the Code. You can't "field-design" these systems. If you do run into an intractible problem, most manufacturers have outstanding technical support and they can usually provide a ready solution. If they can't, then you need to come up with some other code-compliant solution (e.g., run that problem section of the circuit in EMT, to a box, then come back out to the surface raceway) or get special permission from the AHJ.